Method and apparatus for treating cardiac arrhythmia using electrogram features

ABSTRACT

A method and system for ventricular defibrillation by coordinating the delivery of defibrillation shocks with sensed ventricular fibrillation complexes in a way which improves the probability of success of the defibrillation shock. Ventricular electrical activity is monitored in two ventricular locations during ventricular fibrillation to detect coarse ventricular fibrillation complexes and contractions of the ventricular cardiac tissue. The defibrillation shock is delivered in coordination with the occurrence of coarse ventricular fibrillation complexes and the contractions of ventricular cardiac tissue, and specifically to occur on the up-slope portion thereof, for optimal probability of success.

FIELD OF THE INVENTION

This invention pertains generally to implantable medical devices, andmore particularly to implantable medical devices for applyingcoordinated defibrillation electrical energy to the heart.

BACKGROUND OF THE INVENTION

Electric shock defibrillation is a proven technique of treatment of theserious and immediately life-threatening condition of ventricularfibrillation. For patients known to be at risk, an implantabledefibrillator may be used. Such devices contain an energy source, anelectrode lead system in contact in the heart, a sensing system todetect the onset of fibrillation, and a pulse generator for deliveringthe defibrillation shock.

Existing devices are generally designed or programmed to deliver a shockor series of shocks at a fixed interval or intervals following thedetection of the fibrillation, unless fibrillation spontaneouslyterminates on its own first, or until recovery is achieved, as evidencedby the resumption of normal ventricular rhythm. The amount of energy tobe delivered in a shock must be carefully chosen. If too small, it maynot be successful in terminating the fibrillation. On the other hand,the shock must not be so large that it causes damage to the myocardium.The device generally is designed in consideration of the limited energystorage in an implanted device.

Ventricular electrical signals may exhibit a pattern, known as "fineventricular fibrillation" during ventricular fibrillation. The fineventricular fibrillation is characterized by relatively low signalamplitude and lack of organized features. The ventricular electricalsignals may also exhibit a pattern known as "coarse ventricularfibrillation," characterized by intervals of relatively higheramplitude, which may repeat, separated by fine ventricular fibrillationintervals. It has also been suspected that it is easier to defibrillatecoarse ventricular fibrillation than fine ventricular fibrillation.Because of this, previous works have suggested the possibility of timingof defibrillation shocks to features of the ventricular fibrillationwaveforms as a way to improve defibrillation efficacy. However, it hasnot been clear from such prior works, which features are important, andhow to detect and coordinate to them. A need, therefore, exists in theart for a system that improves defibrillation therapy by using theminimal amount of energy necessary to bring about effective andefficient defibrillation.

SUMMARY OF THE INVENTION

The present invention provides an improved defibrillator system. Thedefibrillator system determines an optimal time for the delivery ofdefibrillation shocks, such that the shocks delivered have an improvedprobability of success in terminating the fibrillation. This improvedefficacy provides important medical advantages to the patient, both inthe greater probability of success of individual shocks, and also in thereduction in pulse energy and number of shocks needed to defibrillate.This in turn will result in a smaller implantable defibrillator that candeliver more shocks over the lifetime of the battery.

The defibrillator system detects characteristics of arrhythmia complexeswhich exist during ventricular fibrillation of a heart, and coordinatesthe delivery of ventricular defibrillation shocks with portions of thecomplexes. In one embodiment, the defibrillator system monitors a firstcardiac signal across a first cardiac region. The first cardiac region,in one embodiment, is in a left ventricular cardiac region of the heart.Upon detecting a ventricular fibrillation of the heart, thedefibrillator system delivers a defibrillation shock during, or at thetermination, of a coupling interval time period. The coupling intervaltime period is a preprogrammed time which is started once a contractionof cardiac tissue is detected in the left ventricular cardiac region ofthe heart by the first cardiac signal. In one embodiment, the couplinginterval time period is started once the contractions of cardiac tissuesensed in the first cardiac signal exceeds a predetermined thresholdvalue.

In an additional embodiment for treating ventricular fibrillation, thedefibrillator system monitors the first cardiac signal across the firstcardiac region and a second cardiac signal across a second cardiacregion. In one embodiment, the first cardiac region is a leftventricular cardiac region of the heart and the second cardiac region isa right ventricular cardiac region of the heart. Upon detecting aventricular fibrillation, the defibrillator system deliversdefibrillation shocks during the occurrence of both a coupling intervaltime period started once a contraction of cardiac tissue is detected inthe left ventricular cardiac region of the heart and an up-slope portionof a coarse arrhythmia complex detected in the right ventricular cardiacregion of the heart. Coarse ventricular fibrillation complexes are largeamplitude cardiac electrogram signals detected during a ventricularfibrillation that display regular periodic electrogram wave structures.

In an additional embodiment, the defibrillator system counts the coarseventricular fibrillation complexes detected in the second cardiacsignal. Defibrillation shocks are then coordinated with the up-slopeportion of an nth counted coarse ventricular fibrillation complex havingan amplitude greater than a coarse complex threshold value. The coarsecomplex threshold value is based on a Standard Amplitude Morphology(SAM) value. A SAM value is an average ventricular contraction signalwhich is calculated from a predetermined number of the largest secondcardiac signal peak-to-peak values detected over a predetermined timeinterval. In one embodiment the coarse complex threshold value is 50% ofthe calculated SAM value.

Additionally, the delivery of the defibrillation shock is coordinatedwith a coupling interval time period, which is started once acontraction of cardiac tissue sensed in the first cardiac signal exceedsthe predetermined threshold value. Upon detecting such a signal, thedefibrillator system starts a coupling interval timer which counts offthe predetermined coupling interval time period. In one embodiment, thedelivery of the defibrillation shock is coordinated to occur during thecoupling interval time period for the first cardiac signal and theup-slope portion of the nth counted coarse ventricular fibrillationcomplex of the second signal having an amplitude greater than the coarsecomplex threshold value. In this way the defibrillation shock may becoordinated with a ventricular condition from the first cardiac signaland/or the up-slope portion of a ventricular fibrillation complex fromthe second cardiac signal.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of an embodiment of an implantable cardiacdefibrillator of the type with which the defibrillator system may beimplemented, including a diagrammatic representation of a first leadsystem and a second lead system placed in a heart;

FIG. 2 is a flow chart illustrating a mode of operation of theimplantable cardiac defibrillator of FIG. 1 in detecting tachyarrhythmiaand ventricular fibrillation;

FIG. 3 is a waveform of a morphology signal from a heart in ventricularfibrillation;

FIG. 4 is a waveform of a signal from a heart in ventricularfibrillation;

FIG. 5 is a flow chart illustrating one embodiment of the operation ofthe defibrillator system of FIG. 1 for delivering defibrillation shockscoordinated with ventricular fibrillation features;

FIG. 6 is a waveform of a first signal from a heart in ventricularfibrillation, and illustrating the delivery of the defibrillation shockcoordinated with ventricular fibrillation features of the first signal;

FIG. 7 is a flow chart illustrating the computation of StandardAmplitude of Morphology (SAM) by the defibrillator system;

FIG. 8 is a flow chart illustrating one embodiment of the operation ofthe defibrillator system of FIG. 1 for delivering defibrillation shockscoordinated with ventricular fibrillation features;

FIG. 9 are waveforms of a first and a second signal from a heart inventricular fibrillation, and illustrating the delivery of thedefibrillation shock coordinated with ventricular fibrillation featuresof the first and second signals;

FIG. 10 is a flow chart illustrating one embodiment of the operation ofthe defibrillator system of FIG. 1 for delivering defibrillation shockscoordinated with ventricular fibrillation features; and

FIG. 11 is a waveform of a second signal from a heart in ventricularfibrillation, and illustrating the delivery of the defibrillation shockcoordinated with ventricular fibrillation features of the second signal.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice and use the invention, andit is to be understood that other embodiments may be utilized and thatelectrical, logical, and structural changes may be made withoutdeparting from the spirit and scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense and the scope of the present invention is defined by theappended claims and their equivalents.

One defibrillator system for treating ventricular fibrillation wasprovided in copending U.S. patent application Ser. No. 08/513,685, filedAug. 11, 1995 and now U.S. Pat. No. 5,632,766, which is herebyincorporated by reference in its entirety.

The embodiments of the present invention illustrated herein aredescribed as being included in an implantable cardiac defibrillator,which includes pacing functions and modes known in the art. In analternative embodiment, the present invention is implemented in anexternal defibrillator/monitor. Moreover, other embodiments exist whichdo not depart from the scope and spirit of the present invention.

In FIG. 1, an implantable cardiac defibrillator (ICD) 10 is shown inblock diagram form. It includes terminals, labeled with referencenumbers 12 and 14 for connection to a first lead system 16. The firstlead system 16 is an endocardial lead, although other types of leads,such as epicardial leads, could also be used within the scope of theinvention. The first lead system 16 is adapted for placement in a firstcardiac region of the heart. In one embodiment, the first cardiac regionof the heart is within the coronary sinus and/or the great cardiac veinof the heart adjacent to the left ventricle. The first lead system 16includes a number of electrodes and electrical contacts. A tip electrode18 is located at, or near, the distal end of the first lead system 16,and connects electrically to terminal 12 through a conductor providedwithin the first lead system 16. The first lead system 16 also includesa proximal electrode 20 which is spaced proximal the tip electrode 18.In one embodiment, the proximal electrode 20 is spaced proximal the tipelectrode 18 for placement adjacent to the left ventricle of the heart.The proximal electrode 20 is electrically connected to terminal 14through an internal conductor within the first lead system 16. Theproximal electrode 20 can be of either an annular or a semi-annularconstruction, encircling or semi-encircling the peripheral surface ofthe first lead system 16.

The ICD 10 further includes terminals, labeled with reference numbers22, 24, 26 and 28 for connection to a second lead system 30. The secondlead system 30 is an endocardial lead. The second lead system 30 isadapted for placement within a second cardiac region of the heart. Inone embodiment, the second cardiac region of the heart is the rightventricle of the heart. The second lead system 30 includes a number ofelectrodes and electrical contacts.

A tip electrode 32 is located at, or near, the distal end of the secondlead system 30, and connects electrically through a conductor providedin the lead, for connection to terminal 22. The second lead system 30further includes a first defibrillation coil electrode 34 spacedproximal to the distal end for placement in the right ventricle. Thefirst defibrillation coil electrode 34 is electrically connected to bothterminals 24 and 26 through internal conductors within the body of thesecond lead system 30. The second lead system 30 also includes a seconddefibrillation coil electrode 36, which is spaced apart and proximalfrom the distal end of the second lead system 30 such that the seconddefibrillation coil electrode 36 is positioned within the right atriumor major vein leading to the right atrium of the heart. The seconddefibrillation coil electrode 36 is electrically connected to terminal28 through an internal conductor within the body of the second leadsystem 30.

The ICD 10 is a programmable microprocessor-based system, with amicroprocessor 38 and memory 40, which contains parameters for variouspacing and sensing modes. Pacing modes include, but are not limited to,normal pacing, overdrive or burst pacing, and pacing for prevention ofventricular tachyarrhythmias. Microprocessor 38 further includes meansfor communicating with an internal controller, in the form of an RFreceiver/transmitter 42. This includes a wire loop antenna 44, wherebyit may receive and transmit signals to and from an external controller46. In this manner, programming commands or instructions can betransferred to the microprocessor 38 of the ICD 10 after implant. In oneembodiment operating data is stored in memory 40 during operation. Thisdata may be transferred to the external controller 46 for medicalanalysis.

The tip electrode 18 and the proximal electrode 20, connected throughleads 12 and 14, serve to monitor a first cardiac signal across thefirst cardiac region. The tip electrode 18 and the proximal electrode20, connected through leads 12 and 14, are applied to a sense amplifier48, whose output is shown connected to a threshold level detector 50.These components also serve to sense and amplify signals indicative ofthe QRS waves of the heart, and apply the signals to the microprocessor38.

In one embodiment, the microprocessor 38 responds to the threshold leveldetector 50 by providing pacing signals to a pace output circuit 52, asneeded according to the programmed pacing mode. The pace output circuit52 provides output pacing signals to terminals 12 and 14, which connectsto the tip electrode 18 and the proximal electrode 20, for pacing. Inone embodiment, pacing is provided in the range of 0.1-10 volts. In afurther embodiment, filtering circuitry is incorporated into thecircuitry of FIG. 1 to reduce signal noise from the first cardiacsignal.

In the ICD 10, the tip electrode 32 and the first defibrillation coilelectrode 34, connected through leads 22 and 24, are applied to a senseamplifier 54, whose output is connected to an R-wave detector 56. Thesecomponents serve to amplify and sense the QRS waves of the heart, andapply signals indicative thereof to microprocessor 38. Among otherthings, microprocessor 38 responds to the R-wave detector 56, andprovides pacing signals to a pace output circuit 58, as needed accordingto the programmed pacing mode. Pace output circuit 58 provides outputpacing signals to terminals 22 and 24, which connect to the tipelectrode 32 and the first defibrillation coil electrode 34, for thepacing modes as previously described.

In one embodiment, pacing pulses triggered by the pace output circuit 52and the pace output circuit 58 are controlled by the microprocessor 38to carry out a coordinated pacing scheme at the two ventricular pacinglocations. Pacing modes include, but are not limited to, normal sinusrhythm pacing modes, overdrive or burst pacing modes for treatingventricular tachyarrhythmia, and/or pacing regimens for preventing theonset of a ventricular tachyarrhythmia. Additional advantages forproviding pacing from the two ventricular pacing locations include theability for either one of the two pacing systems to serve as a back-uppacing system and location for the other in the event that one pacingsystem were to fail.

The first defibrillation coil electrode 34 and the second defibrillationcoil electrode 36 serve to monitor a second cardiac signal across thesecond cardiac region. The first and second defibrillation coilelectrodes 34 and 36 are connected through leads 26 and 28 to a senseamplifier 60. The output of the sense amplifier 60 is connected to amorphology analyzer 62 that provides QRS morphology wave signals of theheart to the microprocessor 38. A high-energy output circuit 64 whichoperates under the control of the microprocessor 38, providesdefibrillation level electrical energy to the patient's heart across thefirst defibrillation coil electrode 34 and the second defibrillationcoil electrode 36. Alternatively, the high-energy output circuit 64provides defibrillation level electrical energy to the patient's heartacross either the first and second defibrillation coil electrodes, 34and 36, and the housing of the defibrillator system, where the housingof the defibrillator system is configured as a "hot can" electrode.

FIG. 2 illustrates overall modes of operation of the defibrillatorsystem. In paced operation, the defibrillator system operates underprogrammed control to monitor heart beats occurring in the patient'sheart. This is indicated by block 100 in FIG. 2. Such monitoring isaccomplished through the sense amplifiers 48, 54 and 60, R-wavedetectors 56, threshold level detector 50, and microprocessor 38 controlin FIG. 1. Pacing may be administered as needed, depending upon the typeof pacing functions provided in the ICD 10.

In one embodiment, the defibrillator system treats arrhythmias of aheart, such as ventricular fibrillations by initially monitoring thefirst cardiac signal across the first cardiac region, and the secondcardiac signal across the second cardiac region. Decision block 102tests whether a tachyarrhythmia has been detected. This is done throughanalysis of electrical signals from the heart under control of themicroprocessor 38 and its stored program. In one embodiment, thedecision block 102 uses a rate based determination to indicate theoccurrence of a ventricular tachyarrhythmia. If such condition is notdetected, control branches via path 103 back to the heart beat monitorblock 100, and the process repeats.

If, however, a tachycardia arrhythmia condition is detected at decisionblock 102, control passes via path 105 to decision block 106, whichtests for ventricular fibrillation, through analysis of heart signals asknown in the art. In one embodiment, the determination of ventricularfibrillation is based on the rate of sensed ventricular contractions. Ifventricular fibrillation is not detected, control branches to block 108for ventricular tachyarrhythmia therapies. Ventricular tachyarrhythmiatherapies can include, but are not limited to, the pacing therapiespreviously mentioned. If, however, at block 106, ventricularfibrillation is detected, control branches along path 107 to theventricular fibrillation therapies of FIG. 5, FIGS. 7 and 8, or FIGS. 7and 10 which include coordinated defibrillation shocks as described ingreater detail below.

FIG. 3 illustrates a first cardiac signal such as would be detected bythe sensing amplifier 48, from a first cardiac signal appearing acrossthe proximal electrode 20 and the tip electrode 18 on the first leadsystem 16. For other types of lead systems, similar or correspondingsignals would be present. In FIG. 3, the wave form is an example of avoltage signal at the sense amplifier 48. The vertical axis representsamplitude, and the horizontal axis represents time. The zones designatedas "A" represent active ventricular cardiac tissue in the region of thetip electrode 18 and the proximal electrode 20. Zones designated as "I"represent inactive ventricular cardiac tissue in the region of the tipelectrode 18 and the proximal electrode 20. Within an "A" complex, asingle peak feature of the complex is indicated by reference number 130.The difference in amplitude between the amplitude extremes, 132, 134,indicates the peak-to-peak amplitude calculation which is used as a partof the method of the invention.

FIG. 4 illustrates an electrogram morphology signal from cardiacventricular activity. This second cardiac signal is monitored across thesecond cardiac region. In one embodiment, the second cardiac signal ismonitored between the first defibrillation coil electrode 34 and thesecond defibrillation coil electrode 36 on the second lead system 30.For other types of lead systems, similar or corresponding signals arepresent. In FIG. 4, the wave form is an example of a voltage signal atthe sense amp 60. The vertical axis represents amplitude, and thehorizontal axis represents time. As used herein, the heart (morphology)signals are represented as what is considered as normal polarity ofsignals from the heart. Thus, references to increasing signal, positiveslope, or up-slope, are all with reference to normal polarity. Reversingthe polarity of the leads would cause reversal of the polarity of thesignal, in which case a corresponding reversal of positive slope tonegative slope. If the polarity of sensing is changed, the defibrillatorsystem coordinates defibrillation shocks on negative-going signals. Inone embodiment, the absolute value of the sensed signal could be used,which would correspond to either positive or negative polarity signals.For purposes of the remainder of this detailed description, positive ornormal polarity will be assumed.

In FIG. 4, Zones F1 and F2 show regions of fine ventricularfibrillation. Zones C1 and C2 show coarse ventricular fibrillationcomplexes. Coarse ventricular fibrillation complexes are large amplitudecardiac electrogram signals detected during a ventricular fibrillationthat display regular periodic electrogram wave structures. Withincomplex C1, a single peak feature of the complex is indicated byreference number 150. The difference in amplitude between the amplitudeextremes, 151, 152, indicates the peak-to-peak amplitude. Thepeak-to-peak amplitude values are used in the calculation of a StandardAmplitude Morphology (SAM) value. In one embodiment, the SAM value iscalculated by averaging a predetermined number of the largestpeak-to-peak values detected over a predetermined time interval. Thepredetermined time interval can be programmed within a range of 1-10seconds. Also, the predetermined number of the largest peak-to-peakvalues can be programmed within a range of 3-10. The coarse complexthreshold value is then based on the calculated SAM value, where in oneembodiment the coarse complex threshold value is 50% of the SAM value.

Referring now to FIGS. 5 and 6, there is shown one embodiment of themethod of treating ventricular fibrillation using the defibrillationsystem for delivering coordinated defibrillation shocks based onventricular activity signals from the first cardiac signals. In oneembodiment, the defibrillation system monitors the first cardiac signalacross a left ventricular cardiac region of the heart. Path 107 iscontinued from FIG. 2.

At step 160, a waiting period is initialized, and a waiting period timeris started. The waiting period timer defines the time period duringwhich coordinated defibrillation shocks may be attempted, and afterwhich the defibrillator system will deliver asynchronous defibrillationshocks. This time period is programmable as one of the programmingparameters for the ICD 10 microprocessor 38. This time period must bekept within reasonable physiological limits, before going toasynchronous mode. In one embodiment, the waiting period timer isprogrammed within the range of 10-40 seconds, where 10 seconds is anacceptable value.

Decision block 162, which potentially is looped through multiple times,tests whether the waiting period timer programmed for coordinateddefibrillation shocks has passed. If not, control passes to step 164,where the amplitude of the first cardiac signal for a present or currentpoint detected by the first lead system 16 is taken by sense amplifier48. This could be done by hardware or software in the threshold leveldetector 50, part of which could also be done by software inmicroprocessor 38.

According to one embodiment of the present invention, at step 166 thedefibrillator system tests whether the amplitude of the first cardiacsignal 200 has exceeded a predetermined threshold value 202. Determiningif the a first cardiac signal 200 has exceeded the predeterminedthreshold value 202 is accomplished by comparing the amplitude of thecurrent point of the first cardiac signal 200 to the predeterminedthreshold value 202 programmed into memory 38. The amplitude of thecurrent point of the first cardiac signal 200 is calculated by takingthe difference in amplitude between the signal amplitude extremes 204and 206 of the first signal. The predetermined threshold value 202 canbe programmed in the ranges of 0.1-10 millivolts.

At step 166, if the value of the measured first cardiac signal exceedsthe predetermined threshold value 202, the defibrillator system starts acoupling interval timer at step 168. The coupling interval timer timesout a coupling interval time period 208, during which a coordinateddefibrillation shock 210 can be delivered. Alternatively, thecoordinated defibrillation shock 210 is delivered at the expiration ofthe coupling interval time period 208. The coupling interval period is aprogrammable value in the range of 0-200 milliseconds, where 0-30milliseconds is an acceptable range of values.

At step 170, the defibrillator system tests whether the CI timer hasexpired. If the CI timer has not expired, control passes via 172 to loopthrough step 170 again. After the CI timer has expired, control passesto step 174, which causes the high-energy output circuit 64 to deliverthe defibrillation shock 210.

Alternatively, while the defibrillator system is monitoring the heart,if the waiting period for the defibrillator system times out withoutfinding the required conditions for coordinated defibrillation shocking(i.e, the first cardiac signal does not exceed the predeterminedthreshold value 202), then once the defibrillator system loops back to162 along path 176 control passes via path 178 to step 174 where thedefibrillator system proceeds to deliver an asynchronous defibrillationshock.

Following the delivery of the defibrillation shock, the sensing circuitsof the ICD check to see whether the shock was successful, that is,whether the ventricular fibrillation has stopped. This is represented bya return to point "0" at the start of FIG. 2. If not successful, and ifventricular fibrillation continues, this is detected in FIG. 2, andcontrol passes again to FIG. 5 to repeat the ventricular fibrillationtherapy. In one embodiment, the waiting period (step 162) for the secondor higher passes is by-passed. In one embodiment, the waiting period(step 162) for the second or higher passes is separately programmed fromthe first pass. Then if the first shock fails, the process of sensingand coordination for delivery for a second shock can begin immediately.

In an alternative embodiment, both the first and the second cardiacsignals are used in coordinating the delivery of a defibrillation shockto a heart experiencing ventricular fibrillation. In this embodiment,the defibrillation system monitors a second cardiac signal across aright ventricular region. In FIG. 7, path 107 is continued from FIG. 2.Upon occurrence or detection of a ventricular fibrillation condition,peak-to-peak amplitudes of coarse ventricular fibrillation complexesfrom the second cardiac signal are computed. In one embodiment, thepeak-to-peak amplitudes of coarse ventricular fibrillation complexes arecomputed over a five second interval. The peak-to-peak amplitudes arefrom the second cardiac signals sensed by the sensing amp 60 across thefirst defibrillation coil electrode 34 and the second defibrillationcoil electrode 36. The time duration of five seconds is a programmablevalue, and a different value may be used without departing from thescope of the invention.

At block 220, which is reached after a ventricular fibrillation has beendetected in FIG. 2, a time is initialized at a starting or zero point.The coarse ventricular fibrillation amplitude value for the secondcardiac signal are computed, based upon peak-to-peak value readings, asindicated in FIG. 4, at a computation block 222. This is accomplished bycontinually taking samples of the second ventricular morphology signalsand comparing them with previously obtained samples. When suchcomparison shows a trend reversing, (i.e., from decreasing toincreasing, or from increasing to decreasing in value) for the secondcardiac signal a bottom or top (i.e., a peak, negative or positive) hasbeen reached. Such peak values are then stored for each of the secondventricular morphology signals for comparison with other peak values aspart of the SAM calculation. For each peak occurring in a coarseventricular fibrillation complex, the high and low values, and hence thepeak-to-peak values, are calculated and stored for the second cardiacsignals.

Flow then proceeds to decision block 224, where the time for thefive-second interval is tested. If the five seconds (or otherprogrammable interval) has not passed, flow branches back via path 225to the computation block 222, and computation detection of peaks andcomputation of peak-to-peak value continues. If, however, the time hasexceeded or equaled the five-second set interval, control passes toblock 226. At block 226, the SAM value is calculated for the secondcardiac signal, as being the average of the five largest peak-to-peakmeasurements during the five-second interval in FIG. 4. This is donethrough recall, comparison, and calculation based upon the stored peakvalues for the first cardiac signals.

FIG. 8 shows the operation of the defibrillator system for deliveringcoordinated defibrillation shocks based on ventricular activity signalsfrom the first cardiac signals and on sensed coarse ventricularfibrillation complex features from the second cardiac signals. In oneembodiment, the defibrillation shock is delivered to the heart duringthe occurrence of both a coupling interval time period started once acontraction of cardiac tissue is detected in the left ventricularcardiac region by the first cardiac signal and an up-slope portion of acoarse ventricular fibrillation complex as detected in the rightventricular cardiac region by the second cardiac signal.

The start of FIG. 8 is reached from the flow chart of FIG. 7. In thefollowing embodiment, both the ventricular activity signals of the firstcardiac signals and the sensed coarse ventricular fibrillation complexfeatures of the second cardiac signals are taken into consideration incoordinating a defibrillation shock. At step 240, "n" (the count for aCandidate Morphology Complex discussed below) is set to zero, a waitingperiod is initialized, and a waiting period timer is started. Thewaiting period timer defines the time period during which coordinateddefibrillation shocks may be attempted, and after which thedefibrillator system will deliver asynchronous defibrillation shocks.This time period is programmable as one of the programming parametersfor the ICD 10 microprocessor 38. This time period must be kept withinreasonable physiological limits, before going to asynchronous mode. Inone embodiment, the waiting period timer is programmed within the rangeof 10-40 seconds, where 10 seconds is an acceptable value.

Decision block 242, which potentially is looped through multiple times,tests whether the waiting period timer programmed for coordinateddefibrillation shocks has passed. If not, control passes to step 244where sensed conditions for the first cardiac signal and the secondcardiac signal are assessed to determine if a coordinated defibrillationshock is to be delivered. In one embodiment, the conditions for thefirst cardiac signal and the second cardiac signal are concurrentlyanalyzed at step 244 and both conditions must be satisfied in order forthe defibrillator system to proceed to deliver a defibrillation shock tothe heart at step 246.

In one embodiment, step 244 shows a list of conditions that must bedetected in and satisfied for the first cardiac signal. In the presentembodiment, the conditions monitored from the first cardiac signalinclude whether the first cardiac signal is greater than or equal to apredetermined threshold value and whether a coupling interval timer hasexpired.

The amplitude of the first cardiac signal for a present or current pointdetected by the first lead system 16 is taken by sense amplifier 48.This could be done by hardware or software in the threshold leveldetector 50, part of which could also be done by software inmicroprocessor 38. According to one embodiment of the present invention,at step 244 the defibrillator system concurrently tests whether thefirst cardiac signal has exceeded the predetermined threshold during anepisode of coarse ventricular fibrillation detected in the first cardiacsignal.

In one embodiment, determining if the a first cardiac signal hasexceeded the predetermined threshold is accomplished by comparing theamplitude of the current point of the first cardiac signal to apredetermined amplitude value programmed into memory 40. Thepredetermined threshold value can be programmed in the ranges of 0.1-10millivolts.

Once a first cardiac signal exceeds the predetermined threshold thedefibrillator system starts the coupling interval timer. The couplinginterval timer times out a coupling interval time period, over which acoordinated defibrillation shock can be delivered. The coupling intervaltime period is programmed in the range of 0-200 milliseconds, where 0-30milliseconds is an acceptable range of values.

Step 244 also shows a list of conditions that must be detected in andsatisfied for the second cardiac signal. In the present embodiment, theconditions monitored from the second cardiac signal include whether thesecond cardiac signal is a coarse ventricular fibrillation, with acoarse morphology complex value equal to or greater than a predeterminedvalue and is on an upslope portion of the coarse ventricularfibrillation complex. Other combinations of sensed characteristics fromthe second cardiac signals, however, could be used for coordinating thedelivery of a defibrillation shock with the first cardiac signal.

The amplitude of the morphology of the second cardiac signal detected bythe second lead system 30 is taken by sense amp 60. This could be doneby hardware or software in the morphology analyzer 62, part of whichcould also be done by software in microprocessor 38.

In one embodiment, the defibrillator system counts the occurrences ofcoarse ventricular fibrillation complexes detected in the second cardiacsignal. For the second cardiac signal, the amplitude of the currentpoint is compared to a coarse complex threshold value. If the secondcardiac signal of the current point has a peak-to-peak amplitude greaterthan or equal to the coarse complex threshold value, then the currentpoint is identified as a Candidate Morphology Complex (CMC) for thesecond cardiac signal, and a count "n" of a second signal CMC isincremented by one. In one embodiment of the present invention, thecoarse complex threshold value is 50% of the calculated SAM value.

In an additional embodiment, the value for "n" CMC is a programmablenumber greater than or equal to 2 and less than or equal to about 9. Inthe embodiment shown in FIG. 8, the "n" for the CMC is programmed to 2.At step 146, once the "n" CMC count value is equal to or aboveprogrammed number, the defibrillator system assess the slope of thesecond cardiac signal to determine if the coarse ventricular complexsignal is on an upslope portion of the signal. In one embodiment, thedefibrillator system test whether the current point for the secondcardiac signal is on an up-slope, i.e. having a positive slope bycomparing the amplitude of the current point of the second signal to theamplitude of the previous second signal point, to determine the trend.

In one embodiment, if any of the conditions for either the first cardiacsignal or the second cardiac signal are not satisfied, control branchesto path 247, to repeat the loop. If, however, these conditions are metfor both the first cardiac signal and the second cardiac signal, controlpasses to step 246 where the defibrillator system proceeds to deliver adefibrillation shock. Also, if during this testing process the waitingperiod for the defibrillator system times out without finding therequired conditions for coordinated defibrillation shocking, then oncethe defibrillator system loops back to 242 control passes via path 249to step 246 where the defibrillator system proceeds to deliver anasynchronous defibrillation shock.

FIG. 9 shows an example of the waveforms of the defibrillator systemused for delivering coordinated defibrillation shocks based on sensedcoarse ventricular fibrillation complex features from the first cardiacsignals and from the second cardiac signals. In FIG. 9A, for the firstcardiac signal, the zones labeled "A" are areas of active ventriculartissue and the zones labeled "I" are area of inactive ventriculartissue. In FIG. 9B, for the second cardiac signal, the zones labeled "F"are areas of fine ventricular fibrillation, and the zones labeled "C"are areas of coarse ventricular fibrillation complexes. As theventricular fibrillation is occurring in real time, the defibrillatorsystem is sensing and monitoring the first cardiac signal at the firstcardiac region and the morphology of the second cardiac signal at thesecond cardiac region. For the second cardiac signal, after the firstmajor peak indicated, the defibrillator system has determined that apeak of a possible coarse ventricular fibrillation complex for thesecond cardiac signal has occurred, and the CMC count is incremented atthe peak "n=1". Assume, as is the case in FIG. 9, that it is in fact thestart of a ventricular fibrillation complex. The second peak "n=2" iscounted as 2.

The defibrillator system senses and analyzes the first cardiac signal asit is sensing and analyzing the second cardiac signal. For the firstcardiac signal, after the first active area A1 for the first cardiacsignal has exceeded the predetermined threshold during an episode ofcoarse ventricular fibrillation, the CI timer is started. On the nextup-slope of the second cardiac signal, as the amplitude of an up-slopesignal passes the coarse complex threshold value (in the presentembodiment this value is 50% of the calculated SAM value), on a firstsignal CMC peak count of n=2 or more and with the CI timer not havingbeen exceeded the decision is made based on these criteria to deliverthe defibrillation shock. The microprocessor 38 and high-energy outputcircuit 64 then deliver the shock shortly thereafter based on thisdecision. The defibrillation shock is indicated at line 250.

Following the delivery of the defibrillation shock, the sensing circuitsof the ICD check to see whether the shock was successful, that is,whether the ventricular fibrillation has stopped. This is represented bya return to point "0" at the start of FIG. 2. If not successful, and ifventricular fibrillation continues, this is detected in FIG. 2, andcontrol passes again to FIG. 8 to repeat the ventricular fibrillationtherapy. The waiting period (steps 240, 242) for the second or higherpasses can preferably be by-passed (or at least separately programmedfrom the first pass). Then if the first shock fails, the process ofsensing and coordination for delivery for a second shock can beginimmediately.

In an alternative embodiment, the defibrillator system and method ofdelivering coordinated defibrillation shocks of the present invention isbased either on coarse ventricular fibrillation complex features on leftventricular conditions from the first cardiac signal or from the secondsignal. In this situation, the ventricular fibrillation complexcharacteristics detected by the first signal and the second signal arelogically "OR"ed together in the determination to provide defibrillationshocks. Therefore, if during an episode of ventricular fibrillation thedefibrillator system does not satisfy the left ventricular electrogramcondition (e.g., the amplitude of the first signal does not exceed apredetermined threshold value) and the right ventricular electrogramsignals are coarse, the defibrillator system will deliver coordinateddefibrillation shocks based on the sensed coarse ventricularfibrillation complex features as previously described. Likewise, whenthe left ventricular electrogram condition of the first signal becomesatisfied, but the right ventricular electrogram signal of the secondsignal does not detect the occurrence of coarse ventricular fibrillationcomplexes, the defibrillator system can deliver a defibrillation shockat or before the expiration of the CI timer.

In a further embodiment, additional sensing and/or defibrillationelectrodes are placed in contact with the patient (e.g., subcutaneous,epicardial, and/or endocardial electrodes) and electrically coupled tothe ICD 10. The additional sensing and/or defibrillation electrodes areused in sensing cardiac morphology signals from the left ventriclebetween the electrodes on the first lead system 20 and the additionalsensing and/or defibrillation electrodes. The morphology signals fromthe first lead system 16 located in the left ventricular region areprocessed as the morphology signals from the second lead system 30,where the nth counted coarse ventricular fibrillation in the secondsignal (i.e., the CMC count) further includes an mth counted coarseventricular fibrillation in the first signal. The mth counted coarseventricular fibrillation is a programmable number which is greater thanor equal to 2 and less than or equal to 9.

The first and second morphology signals are then used to base thedelivery of defibrillation shocks to a heart experiencing ventricularfibrillation. For example, during a detected ventricular fibrillationepisode SAM values (first and second predetermined values for the firstand second signals) and CMC values (mth and nth values for the first andsecond signals) are calculated for both the first and the second cardiacsignals and utilized by the defibrillator system to base the delivery ofa defibrillation shock. It is, therefore, possible to coordinatedefibrillation shocks to be delivered when, for example, bothventricular morphology signals indicating a coarse ventricularfibrillation complex have satisfied their CMC value requirements andboth coarse ventricular fibrillation signals are on an up-slope portionof their respective signals. Alternatively, one signal's up-slopeportion could be programmed to be a dominate signal and thedefibrillation shock would be delivered regardless of the slope of theother morphology signal.

Referring now to FIG. 10, there is shown an alternative embodiment of amethod and operation of treating ventricular fibrillation by deliveringcoordinated defibrillation shocks based on monitored second cardiacsignals. In one embodiment, the defibrillation shock is delivered to theheart experiencing a ventricular fibrillation during the occurrence of awaiting period timer and an up-slope portion of a coarse ventricularfibrillation complex as detected in the second cardiac region by thesecond cardiac signal.

The start of FIG. 10 is reached from the flow chart of FIG. 7. In thefollowing embodiment, the sensed coarse ventricular fibrillation complexfeatures of the second cardiac signals are taken into consideration incoordinating a defibrillation shock. At step 252, "n" (the count for aCandidate Morphology Complex discussed below) is set to zero, a waitingperiod is initialized, and a waiting period timer is started once aventricular fibrillation has been detected. The waiting period timerdefines the time period during which coordinated defibrillation shocksmay be attempted, and after which the defibrillator system will deliverasynchronous defibrillation shocks. This time period is programmable asone of the programming parameters for the ICD 10 microprocessor 38. Thistime period must be kept within reasonable physiological limits, beforegoing to asynchronous mode. In one embodiment, the waiting period timeris a programmable value within the range of 10-40 seconds, where 10seconds is an acceptable value.

Decision block 254, which potentially is looped through multiple times,tests whether the waiting period timer programmed for coordinateddefibrillation shocks has passed. If not, control passes to step 256,where the defibrillation system monitors a signal representative ofventricular electrical activity during a period of ventricularfibrillation. In one embodiment, if the defibrillation system detects inthe monitored signal the occurrence of coarse ventricular fibrillationcomplexes, the defibrillation system then analyzes the coarseventricular fibrillation complexes to determine an upslope, and deliversa defibrillation shock either during the upslope portion of a coarseventricular fibrillation complex or at the expiration of the waitingperiod timer. where sensed conditions for the second cardiac signal isassessed to determine if a coordinated defibrillation shock is to bedelivered. Therefore, at step 256 the conditions detected in the secondcardiac signal must be satisfied in order for the defibrillator systemto proceed to deliver a defibrillation shock to the heart at step 258.

In one embodiment, step 256 shows a list of conditions that must bedetected in and satisfied for the second cardiac signal. The conditionsdetected in the monitored second cardiac signal include whether thesecond cardiac signal is a coarse ventricular fibrillation, with acoarse morphology complex value equal to or greater than a predeterminedvalue and is on an upslope portion of the coarse ventricularfibrillation complex.

The amplitude of the morphology of the second cardiac signal detected bythe second lead system 30 is taken by sense amp 60. This could be doneby hardware or software in the morphology analyzer 62, part of whichcould also be done by software in microprocessor 38. In the presentembodiment, the defibrillator system monitors the morphology signalacross the first defibrillation coil electrode 34 and the seconddefibrillation coil electrode 36 of the second lead system 30.

In one embodiment, the defibrillator system counts the occurrences ofcoarse ventricular fibrillation complexes detected in the second cardiacsignal, and either coordinates the delivery of the defibrillation shockwith the upslope portion of a predetermined numbered occurrence ofcoarse ventricular fibrillation complexes or at the expiration of thewaiting period timer. In one embodiment, the defibrillation shock isdelivered to the heart by applying a pulse of electrical energy to thesecond lead system 30 and across the heart.

For the second cardiac signal, the amplitude of the current point iscompared to a coarse complex threshold value. If the second cardiacsignal of the current point has a peak-to-peak amplitude greater than orequal to the coarse complex threshold value, then the current point isidentified as a Candidate Morphology Complex (CMC) for the secondcardiac signal, and a count "n" of a second signal CMC is incremented byone. In one embodiment of the present invention, the coarse complexthreshold value is 50% of the calculated SAM value.

In an additional embodiment, the value for "n" CMC is a programmablenumber greater than or equal to 2 and less than or equal to about 9. Inthe embodiment shown in FIG. 10, the "n" for the CMC is programmed to 2.At step 256, once the "n" CMC count value is equal to or aboveprogrammed number, the defibrillator system analyzes the coarseventricular fibrillation detected in the second cardiac signal todetermine if the coarse ventricular complex signal is on an upslopeportion of the signal. In one embodiment, the defibrillator system testwhether the current point for the second cardiac signal is on anup-slope, i.e. having a positive slope by comparing the amplitude of thecurrent point of the second signal to the amplitude of the previoussecond signal point, to determine the trend.

In one embodiment, if any of the conditions for the second cardiacsignal is not satisfied, control branches to path 260, to repeat theloop. If, however, these conditions are met for the second cardiacsignal, control passes to step 258 where the defibrillator systemproceeds to deliver a defibrillation shock. Also, if during this testingprocess the waiting period for the defibrillator system times outwithout finding the required conditions for coordinated defibrillationshocking, then once the defibrillator system loops back to 254 controlpasses via path 262 to step 258 where the defibrillator system proceedsto deliver an asynchronous defibrillation shock.

FIG. 11 shows an example of the waveforms of the defibrillator systemused for delivering coordinated defibrillation shocks based on sensedcoarse ventricular fibrillation complex features from the second cardiacsignals. For the second cardiac signal, the zones labeled "F" are areasof fine ventricular fibrillation, and the zones labeled "C" are areas ofcoarse ventricular fibrillation complexes. As the ventricularfibrillation is occurring in real time, the defibrillator system issensing and monitoring the morphology of the second cardiac signal atthe second cardiac region. For the second cardiac signal, after thefirst major peak indicated, the defibrillator system has determined thata peak of a possible coarse ventricular fibrillation complex for thesecond cardiac signal has occurred, and the CMC count is incremented atthe peak "n=1".

Assume, as is the case in FIG. 11, that it is in fact the start of aventricular fibrillation complex. On the next up-slope of the secondcardiac signal, as the amplitude of an up-slope signal passes the coarsecomplex threshold value (in the present embodiment this value is 50% ofthe calculated SAM value), on a first signal CMC peak count of n=2 ormore the decision is made based on these criteria to deliver thedefibrillation shock. The microprocessor 38 and high-energy outputcircuit 64 then deliver the shock shortly thereafter based on thisdecision. The defibrillation shock is indicated at line 262.

Following the delivery of the defibrillation shock, the sensing circuitsof the ICD check to see whether the shock was successful, that is,whether the ventricular fibrillation has stopped. This is represented bya return to point "0" at the start of FIG. 2. If not successful, and ifventricular fibrillation continues, this is detected in FIG. 2, andcontrol passes again to FIG. 10 to repeat the ventricular fibrillationtherapy. The waiting period (step 254) for the second or higher passescan preferably be by-passed (or at least separately programmed from thefirst pass). Then if the first shock fails, the process of sensing andcoordination for delivery for a second shock can begin immediately.

We claim:
 1. A method, comprisingmonitoring a first cardiac signalacross a left ventricular cardiac region; detecting a contraction ofcardiac tissue in the left ventricular cardiac region in the firstcardiac signal; starting a coupling interval timer once the contractionof cardiac tissue is detected where the coupling interval timer counts apredetermined time period; and delivering a defibrillation shock duringthe occurrence of the coupling interval time period.
 2. The method ofclaim 1, including determining whether the first cardiac signal exceedsa predetermined threshold value, and starting the coupling interval timeperiod once the first cardiac signal exceeds the predetermined thresholdvalue.
 3. The method of claim 2, including programming the predeterminedthreshold value in the range of 0.1 to 10 millivolts.
 4. The method ofclaim 1, including programming the coupling interval time period in therange of 0 to 200 milliseconds.
 5. The method of claim 1, where the stepof monitoring further includes monitoring a second cardiac signal acrossa right ventricular cardiac region, and the step of delivering adefibrillation shock further includes delivering the defibrillationshock during the occurrence of both the coupling interval time periodstarted once a contraction of cardiac tissue is detected in the leftventricular cardiac region by the first cardiac signal and an up-slopeportion of a coarse ventricular fibrillation complex as detected in theright ventricular cardiac region by the second cardiac signal.
 6. Themethod of claim 5, further including the step of counting coarseventricular fibrillation complexes detected in second cardiac signal. 7.The method of claim 6, further including the step of coordinating thedelivery of the defibrillation shock with the up-slope portion of an nthcounted coarse ventricular fibrillation complex detected in the secondcardiac signal.
 8. The method of claim 7, where the nth counted coarseventricular fibrillation complex is a number greater than or equal to 2and less than or equal to about
 9. 9. The method of claim 7, where thedelivery of the defibrillation shock is further coordinated the nthcoarse ventricular fibrillation complex having an amplitude greater thana coarse complex threshold value.
 10. The method of claim 5, where thestep of delivering a defibrillation shock occurs during the couplinginterval time period started once the first cardiac signal exceeds apredetermined threshold value and a second cardiac signal having acoarse ventricular fibrillation complex amplitude greater than a coarsecomplex threshold value.
 11. The method of claim 10, further includingthe steps of counting coarse ventricular fibrillation complexes detectedin the second cardiac signal and coordinating the delivery of thedefibrillation shock with the up-slope portion of an nth counted coarseventricular fibrillation complex detected in the second cardiac signal,where the nth counted coarse ventricular fibrillation complex is anumber greater than or equal to 2 and less than or equal to about
 9. 12.The method of claim 1, further including delivering pacing level pulseof electrical energy at the left ventricular cardiac region of theheart.
 13. The method of claim 12, including providing normal sinuspacing to the heart for the pacing level pulses of electrical energy.14. The method of claim 12, including providing overdrive pacing to theheart for the pacing level pulses of electrical energy.
 15. The methodof claim 1, including detecting a ventricular fibrillation;starting awaiting period timer once the ventricular fibrillation is detected;analyzing whether the defibrillation shock delivered during theoccurrence of the coupling interval time period terminated theventricular fibrillation; and delivering at least one asynchronousdefibrillation shock if the ventricular fibrillation is not terminatedby the delivery of one or more of the defibrillation shocks.